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Abstract

We present a simple to process tunable laser, fabricated in a low-cost generic fabrication process and based on two coupled Fabry-Perot cavities. The complex coupling coefficients of the coupling element are analytically derived from a 3×3 MMI using coupled mode theory and chosen to maximize the SMSR during lasing operation. Additionally, one of the cavities contains a reflective interferometer, which acts as coarse wavelength selector. This interferometer is derived from a Michelson Interferometer, by replacing the two independent mirrors with our optimized coupling element, leading to a doubled Free Spectral Range. As a result, we obtained a tuning range of 26 nm with potential for beyond 40 nm, a SMSR larger than 40 dB and fiber coupled power up to 9 dBm.

Figures (11)

Fig. 1 Schematic of extended CCL with coupling element and novel reflective interferometric device outlined by the dashed box. Cx, and Cb denote the complex coupling coefficients between the cavities. The two integrated mirrors with reflectivity r2 are identical components and introduced in more detail in section 3.

Fig. 2 A schematic of a 3×3 MMI, followed by BPM simulations of the device of 10 µm width under different excitations of the input. The first simulation shows single input excitation (b), after which the two outer inputs are excited with a phase difference of π (c) and 0 (d). The dashed lines in (c) and (d) represent a 45 degree corner to form the integrated mirror.

Fig. 7 Threshold gain ratio between main mode and next two competitors for different reflectivities of coupling mirror r2. Solid lines are the closest side mode, while dashed lines represent the competitor one combined FSR away. The output of the laser is formed by a facet with r1 = 0.55 and the interferometer follows |r3|2 = |r2|2(|Cb|sin(kLM) + |Cx|)2, where ΔLM is the arm-length difference in the interferometer and r2, |Cb|=0.79 and |Cx|=0.21 are reflectivity and coupling coefficients of the integrated mirror

Fig. 8 Microscope image of the fabricated Coupled Cavity Laser which contains the interferometer as tunable coarse wavelength filter. The geometry of the device is given in the beginning of section 6 in more detail.

Fig. 9 (a) LI curves when the main cavity current is altered, while the external cavity is kept constant. The legend indicates the value in mA. (b) Spectrum of laser when each SOA is biased with 90 mA.

Fig. 11 (a)Measured photo current when cavity phase sections are altered for different SOA currents. (b)Recorded spectra with settings deduced from the minimization of the photo current for different SOA currents.